The crowdsanywhere from 2,000 to 20,000 worshippers each weekendcan be an attractive target for a deranged shooter. Overflowing offering plates are tempting to thieves, and well-known preachers can become high-profile targets.

Sunday's shootings at New Life Church in Colorado Springs and a missionary training facility in Arvada, Colo. which left five people dead, including a gunmanreflect the security nightmares facing some of the country's largest churches. Many of those churches now employ armed guards to protect human, financial and physical "assets."

Brady Boyd, the senior pastor at New Life Church, said an armed guard "probably saved over 100 lives" when she shot and killed the gunman just inside the doors of the Colorado church.

"That's the reality of our world," he told reporters Monday. "I don't think any of us grew up in churches where that was a reality, but today it is."

Boyd said the volunteer guard was put in position after the church heard about the shootings in Arvada. The church has about 15 or 20 guards, some armed, and the guard who killed the gunman used her personal weapon, he said.

Violent crimes remain extremely rare at U.S. churches. Eric Spacek, a senior church risk manager for the GuideOne Center for Risk Management in West Des Moines, Iowa, said crime accounts for just 5 percent of all claims filed by the 40,000 churches insured by GuideOne.

Still, the growth of megachurches has spawned an entire industry devoted to protecting and securing crowds that can be larger than some towns or shopping malls.